Apparatus and method for operating multiple beamforming transceiver in wireless communication system

ABSTRACT

A method for operating a base station in a wireless communication system in order to support a plurality of propagation characteristics is provided. The method includes allocating resource periods for respective propagation characteristics, transmitting system information including information on the propagation characteristics, transmitting a reference signal with the propagation characteristic corresponding to the relevant resource period through at least one of the resource periods, and receiving feedback information determining channel qualities for all of the propagation characteristics.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed on Sep. 19, 2011 in the Korean IntellectualProperty Office and assigned Serial No. 10-2011-0093845, the entiredisclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system.

2. Description of the Related Art

In order to satisfy an increasing demand for wireless data traffic,wireless communication systems are developing to support a higher datatransmission rate. The 4th Generation (4G) system, which is starting tobe commercialized, has been developed mainly to improve spectralefficiency in order to increase a data transmission rate. However, ithas become difficult to satisfy an explosively-increasing demand forwireless data traffic solely by the spectral efficiency improvementtechnology.

As a scheme for addressing the above problem, there is a scheme forusing a very wide frequency band. A frequency band used in the currentmobile cellular system is generally lower than 10 GHz, and it is verydifficult to secure a wide frequency band. There is therefore a need tosecure broadband frequencies in a higher frequency band. However, as anoperation frequency band for wireless communication becomes higher, apropagation path loss increases. Thus, a wave propagation distancedecreases, and a service coverage area decreases accordingly.Beamforming is a technology for addressing this problem, that is, forreducing a propagation path loss and increasing a wave propagationdistance.

In general, beamforming concentrates a wave propagation region in aspecific direction by using a plurality of antennas, or increases thedirectivity of reception sensitivity in a specific direction. Herein, agroup of a plurality of antennas may be referred to as an antenna array,and each antenna included in the antenna array may be referred to as anarray element. The antenna array may be configured in various types suchas a linear array and a planar array. When beamforming is used, atransmission distance is increased by an increased signal directivityand a signal is hardly transmitted in directions other than thedirection of directivity. Therefore, an interference caused by othersignals is greatly reduced. On the other hand, since the multipathcharacteristic of a channel is reduced due to beamforming, it isdifficult to support transmission diversity.

Thus, in applying beamforming, it is preferable to determine whether toperform beamforming in consideration of the communication environmentand channel characteristics, or perform a suitable type of beamforming.What is therefore desired is an alternative method for supporting andoperating beamforming schemes with different propagation characteristicsin wireless communication systems.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages below. Accordingly, an aspect of the present invention isto provide an apparatus and method for supporting different propagationcharacteristics in a wireless communication system.

Another aspect of the present invention is to provide an apparatus andmethod for selecting an optimal propagation characteristic in a wirelesscommunication system.

Another aspect of the present invention is to provide an apparatus andmethod for transmitting information on propagation characteristicsoperated in a wireless communication system.

Another aspect of the present invention is to provide an apparatus andmethod for transmitting feedback information used to select an optimalpropagation characteristic in a wireless communication system.

In accordance with an aspect of the present invention, a method foroperating a base station in a wireless communication system is provided.The method includes allocating resource periods for respectivepropagation characteristics, transmitting system information includinginformation on the propagation characteristics, transmitting a referencesignal with the propagation characteristic corresponding to the relevantresource period through at least one of the resource periods, andreceiving feedback information determining channel qualities for all ofthe propagation characteristics.

In accordance with another aspect of the present invention, a method foroperating a terminal in a wireless communication system is provided. Themethod includes receiving system information including information onpropagation characteristics operated in a base station, detecting anallocation of resource periods for the propagation characteristicsthrough the system information, detecting a reference signal with apropagation characteristic corresponding to a relevant resource periodthrough at least one of the resource periods, and transmitting feedbackinformation determining channel qualities for all of the propagationcharacteristics.

In accordance with another aspect of the present invention, an apparatusof a base station in a wireless communication system is provided. Theapparatus includes a control unit for allocating resource periods forrespective propagation characteristics, and a modem for transmittingsystem information including information on the propagationcharacteristics, transmitting a reference signal with the propagationcharacteristic corresponding to the relevant resource period through atleast one of the resource periods, and receiving feedback informationdetermining channel qualities for all of the propagationcharacteristics.

In accordance with another aspect of the present invention, an apparatusof a terminal in a wireless communication system is provided. Theapparatus includes a modem receiving system information includinginformation on propagation characteristics operated in a base station,and a control unit detecting an allocation of resource periods for thepropagation characteristics through the system information, wherein themodem detects a reference signal with a propagation characteristiccorresponding to a relevant resource period through at least one of theresource periods, and transmits feedback information determining channelqualities for all of the propagation characteristics.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following description whentaken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are diagrams illustrating examples of beam patterns withdifferent beamwidths in a wireless communication system according to anexemplary embodiment of the present invention;

FIG. 2 is a diagram illustrating an example of the use of beamwidthsdepending on data characteristics in a wireless communication systemaccording to an exemplary embodiment of the present invention;

FIG. 3 is a diagram illustrating an example of the use of beamwidthsdepending on cell characteristics in a wireless communication systemaccording to an exemplary embodiment of the present invention;

FIG. 4 is a diagram illustrating an example of the use of polarizationcharacteristics in a wireless communication system according to anexemplary embodiment of the present invention;

FIG. 5 is a diagram illustrating examples of reference signal andchannel information feedback in a wireless communication systemaccording to an exemplary embodiment of the present invention;

FIG. 6 is a diagram illustrating examples of reference signal andchannel information feedback in a wireless communication systemaccording to another exemplary embodiment of the present invention;

FIG. 7 is a flow diagram illustrating a process of operating a basestation in a wireless communication system according to an exemplaryembodiment of the present invention;

FIG. 8 is a flow diagram illustrating a process of operating a terminalin a wireless communication system according to an exemplary embodimentof the present invention;

FIG. 9 is a block diagram illustrating a configuration of a base stationin a wireless communication system according to an exemplary embodimentof the present invention; and

FIG. 10 is a block diagram illustrating a configuration of a terminal ina wireless communication system according to an exemplary embodiment ofthe present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

More particularly, the present invention relates to an apparatus andmethod for operating multiple beamforming transceivers with differentcharacteristics in a wireless communication system. Hereinafter,technologies for supporting beamforming schemes with differentpropagation characteristics in a wireless communication system accordingto exemplary embodiments of the present invention will be described.

A wireless communication system according to an exemplary embodiment ofthe present invention operates based on beamforming, and appliesdifferent propagation characteristics according to the utilization andpurpose of a transmission (TX) signal. In addition, the wirelesscommunication system according to an exemplary embodiment of the presentinvention may apply different propagation characteristics according tolink characteristics. Accordingly, the present disclosure describesinformation used to operate different propagation characteristics, aprocess of selecting different propagation characteristics based on theinformation, an operation and configuration of a base station fortransmitting signals having the coexistence of different propagationcharacteristics, and an operation and configuration of a terminalreceiving signals having the coexistence of different propagationcharacteristics.

Propagation characteristics considered in the present disclosure arecharacteristics of signals transmitted/received through antennas. Forexample, the propagation characteristics include physicalcharacteristics of waves and propagation characteristics depending ontransmission/reception (TX/RX) antenna structures. Specifically, thephysical characteristics of waves include polarization (or polarizedwave) characteristics and the amplitude (e.g., strength) of a wave, andthe propagation characteristics depending on TX/RX antenna structuresinclude a beam pattern. The polarization characteristics are generallyclassified into linear polarization (e.g., linearly polarized wave) andcircular polarization (e.g., circularly polarized wave) according to thepropagation direction of a wave and the form of a generated electricfield.

The characteristics of signals vary according to the propagationcharacteristics. Thus, signals with different propagationcharacteristics may be used according to the purposes of systems. Forexample, as for the beam pattern that is one of the propagationcharacteristics depending on TX/RX antenna structures, a narrowbeamwidth and a wide beamwidth provide different channel propagationeffects.

FIGS. 1A and 1B illustrate examples of beam patterns with differentbeamwidths in a wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIGS. 1A and 1B, FIG. 1A illustrates a beam pattern with awide beamwidth, and FIG. 1B illustrates a beam pattern with a narrowbeamwidth.

The propagation characteristics depending on beamwidths are as follows.If a beam pattern has a wide beamwidth, a signal radiated from anantenna undergoes a spatially wide channel. An example of an extremelywide beamwidth is an isotropic pattern that is radiated uniformly in alldirections. A sector antenna of a base station used in a mobilecommunication system of the related art uses a beam pattern covering theentire range of an angle corresponding to one sector around the sectorantenna.

As for a signal with a wide beamwidth, since the effect of spatiallyconcentrating the energy of a signal radiated from an antenna is small,an antenna gain is not relatively large. However, the propagation of asignal through a spatially wide channel increases the probability ofgenerating independent signal paths between a TX antenna and an RXantenna.

On the other hand, if a beam pattern has a narrow beamwidth, a signalradiated from an antenna undergoes a spatially narrow channel. In thiscase, since the effect of spatially concentrating the energy of aradiated signal is large, an antenna gain is relatively large. However,the propagation of a signal through a spatially narrow channel reducesthe probability of generating independent signal paths between a TXantenna and an RX antenna.

Hereinafter, examples of the use of different propagationcharacteristics according to exemplary embodiments of the presentinvention will be described.

Different beamwidth characteristics may be used as follows. If thesystem supports only a wide beamwidth, an antenna gain is low.Therefore, the capability of compensating for a large path loss in anultra-high frequency band is greatly degraded. Accordingly, the size ofa cell region is greatly reduced. On the other hand, if the systemsupports only a narrow beamwidth, a point-to-point link channel capacityis improved. However, the efficiency of transmitting control informationsuch as a reference signal and broadcast information usingpoint-to-multipoint transmission is low, and an overhead is increased.Thus, it is efficient for the system to use signals with differentbeamwidths according to the purposes and characteristics of signalstransmitted.

For example, as described below with reference to FIG. 2, a signalunicast to a terminal may be beam-formed into a narrow beam, and asignal broadcast or multicast to a plurality of terminals may bebeam-formed into a wide beam.

FIG. 2 illustrates an example of the use of beamwidths depending on datacharacteristics in a wireless communication system according to anexemplary embodiment of the present invention.

Referring to FIG. 2, a base station 210 transmits unicast data to aterminal A 221, and transmits multicast data or broadcast data to theterminal A 221, a terminal B 222, and a terminal C 223. In this case,the base station 210 forms a narrow-beamwidth signal 231 in order totransmit unicast data to the terminal A 221, and forms a wide-beamwidthsignal 232 in order to transmit multicast data or broadcast data to theterminals. However, even in the case of the multicast data or thebroadcast data, if the terminal A 221, the terminal B 222, and theterminal C 223 are concentrated in a narrow region, the base station 210may form a narrow-beamwidth signal.

Also, different beamwidth characteristics may be used as follows. Anoutdoor macro base station and an indoor femto base station may usedifferent beamwidth characteristics. The macro base station provides aservice in a cell that is relatively wide and open. Thus, in the cell, apropagation shadow area may be generated due to structures such asbuildings. Thus, the macro base station may use narrow-beamwidthpropagation characteristics by considering the size of a cell, thedistance from a terminal, and the channel condition of a terminal. Thefemto base station is a small-sized base station installed in apropagation shadow area (such as a home or an office) of the macro basestation, and provides a service only in an area that is smaller incomparison with a macro cell. Thus, the femto base station can secure acell region even by a signal with wide-beamwidth propagationcharacteristics, and therefore has no need to increase an overhead byusing a narrow-beamwidth signal. Thus, as described below with referenceto FIG. 3, different beamwidths can be used according to cellcharacteristics.

FIG. 3 illustrates an example of the use of beamwidths depending on cellcharacteristics in a wireless communication system according to anexemplary embodiment of the present invention.

Referring to FIG. 3, a macro base station 311 uses a narrow beam 331 tocommunicate with terminal A 321, and a femto base station 312 uses awide beam 332 to communicate with terminal B 322.

In addition, in an environment where a link quality is good even when awide beamwidth is used, for example, an environment where the distancebetween a base station and a terminal is not long, specifically, in thecase of the femto base station, the base station can supportMultiple-Input Multiple-Output (MIMO) transmission by using a signalwith a wider beamwidth. To this end, the base station may feed backinformation from a user (such as a channel quality and a preferred MIMOtransmission technique), determine a data transmission scheme accordingto the fed-back information, determine a propagation characteristicsuitable for the determined data transmission scheme, and thentransmit/receive signals. In this case, the entire resource may bedivided to set periods to which different propagation characteristicsare applied, and information on period allocation may be notified to aterminal.

Different polarization characteristics may be used as follows.Polarization is determined by the type of an antenna radiating a wave.The system may improve communication performance by actively using thepolarization characteristics. For example, the system may use the factthat signals with different polarization characteristics are small inmutual interference at reception. The polarization characteristics havethe greatest influence when a channel between a base station and aterminal is Line-of-Sight (LoS). Thus, to a terminal in a LoS channelenvironment, the base station may transmit a signal with a polarizationcharacteristic different from polarization characteristics of a signalto other terminals.

For example, as described below with reference to FIG. 4, signals withdifferent polarization characteristics may be transmitted to respectiveterminals.

FIG. 4 illustrates an example of the use of polarization characteristicsin a wireless communication system according to an exemplary embodimentof the present invention.

Referring to FIG. 4, a base station 410 transmits acircular-polarization signal 431 to a terminal A 421, and transmits alinear-polarization signal 432 to a terminal B 422. To this end, thebase station 410 may include a first antenna generating a circularpolarization and a second antenna generating a linear polarization. Bymore actively using the fact that a mutual interference is small whenthe polarization characteristics are different, the base station 410 maytransmit signals 431 and 432 with different polarization characteristicsthrough the same resources (e.g., frequency resources and timeresources). In this case, since resource use efficiency increases,system capacity is expected to increase.

A scheme based on the polarization characteristics is more advantageousas the number of propagation paths decreases. Therefore, the scheme issuitable for an environment where a narrow-beamwidth signal is used.However, since propagation path characteristics are different betweenusers, a base station should select a user to which polarizationcharacteristics are to be applied, and should feed back channelinformation from a user in selecting the user. Also, when polarizationcharacteristics are used as described above, the base station shouldnotify the terminal of the polarization characteristics applied to theterminal.

According to the above examples of the use of propagationcharacteristics, the system may be operated as follows.

A base station supports a plurality of beam patterns, and applies aspecific beam pattern with discrimination between a control channel anda data channel. To this end, the base station has the capability ofgenerating a plurality of beam patterns. For example, when using anarray antenna including a plurality of antenna elements, a base stationmay control a beamwidth by the number of elements used for signalradiation. When desiring to form a narrow beam, the base stationradiates a signal through all the antenna elements. In this case, sincethe antenna gain of a main lobe of a beam pattern is relatively large, asignal may have relatively large power when received at an RX terminalthrough a channel. Accordingly, a received signal strength of a linkincreases. On the other hand, when desiring to form a wide beam, thebase station radiates a signal through only some of the antenna elementsin an exemplary embodiment. In this case, since the antenna gain of amain lobe of a beam pattern is relatively small, a received signalstrength of a link is small. As another example, a base station maycontrol a beamwidth by using the phase and amplitude of a signalcontrolled by each antenna element. As yet another example, a basestation may control a beam pattern and a beamwidth by using a basebanddigital precoder and a Radio Frequency (RF) analog beamformer together.

As for a beam pattern with a narrow beamwidth, since a signal iseffectively transmitted only to a spatially narrow area, it is notsuitable for simultaneous reception by a plurality of terminals. On theother hand, as for a beam pattern with a wide beamwidth, since a signalis effectively transmitted to a spatially wide area, it is suitable forsimultaneous reception by a plurality of terminals. Thus, a signaltransmitted to a plurality of terminals distributed over a wide area maybe transmitted by a beam pattern with a wide beamwidth, and a signaltransmitted to one terminal or a small number of terminals located in anarrow area may be transmitted by a beam pattern with a narrowbeamwidth.

Thus, a beam pattern may be applied differently according to whether achannel is for point-to-point communication. Specifically, the systemmay apply a narrow-beamwidth beam pattern to a channel forpoint-to-point communication and apply a wide-beamwidth beam pattern toa channel for point-to-multipoint communication or broadcasting.Examples of the channel for point-to-point communication include aunicast data channel and a unicast control channel. Examples of thechannel for point-to-multipoint communication or broadcasting include achannel for transmission of system information to a plurality ofterminals, a synchronization channel for acquisition of time/frequencysynchronization of a terminal, and a broadcast channel for informationtransmitted to terminals in the system.

Also, a base station may change a beam pattern according to the currentcondition of a terminal. Examples of the beam pattern change are asfollows.

For example, while a terminal receives a data channel at a distance froma base station by using a beam pattern with a narrow beamwidth, when apath loss decreases due to the approach of the terminal to the basestation, the base station may increase an Adaptive Modulation and Coding(AMC) level to increase transmission efficiency and improve systemperformance. However, the maximum efficiency of AMC with respect to onestream is determined by a modulation order and a coding rate thereofThus, when a path loss decreases in excess of the maximum AMCtransmission efficiency, the terminal may request application of a beampattern with a beamwidth wider than a current beamwidth, or may notify acurrent condition to the base station, so that the base station appliesa beam pattern with a wider beamwidth.

As another example, while a terminal receives a data channel by using abeam pattern with a narrow beamwidth, when RX power decreases rapidlydue to the interruption of a signal path by an obstacle, the terminalmay request a change into a TX beam headed in a different direction.However, when a path loss of the TX beam headed in a different directionis not satisfactory due to an obstacle, the terminal may requestapplication of a beam pattern with a wide beamwidth, or may notify acurrent condition to the base station, so that the base station appliesa beam pattern with a wider beamwidth.

As described above, the system may improve the system performance byapplying an optimal beam pattern according to the type of a channel, thecondition of a terminal, and a communication environment. When thesystem is operated by using different beam patterns, a base stationshould provide terminals with information related to a current beampattern so that smooth communication can be performed by allowing theterminal to be preferentially notified of the use amount and the usemethod of resources varying according to beam patterns.

An example of beam pattern information provided by a base station is asfollows. As the degree of a narrow beamwidth varies, the number of timesof transmitting a reference signal for covering all the areas in a cellmay vary. For example, if an azimuth angle in a cell is represented in360 degrees, when a wave having the characteristics of a beam patternwith a beamwidth of 10 degrees is used, the transmission of a referencesignal in different directions at least 36 times is performed. Asanother example, when a cell is divided into three sectors and eachsector has an azimuth angle of 120 degrees, the transmission of areference signal in each sector at least 12 times is performed. As yetanother example, when a wave having the characteristics of a beampattern with a beamwidth of 30 degrees is used, the transmission of areference signal at least 12 times is required in a 360-degree cell andthe transmission of a reference signal at least 4 times is required in a120-degree sector. For example, the number of times of transmitting areference signal varies by a beamwidth, and the amount of resources usedto transmit the reference signal varies accordingly. Thus, informationindicating the number of times of transmitting the reference signalshould be provided to the terminal. Herein, the reference signal mayalso be referred to as ‘synchronization signal’, ‘preamble’, ‘midamble’,‘pilot signal’, or the like.

Another example of beam pattern information provided by a base stationis as follows. A terminal should estimate a path loss of a signal from abase station. The path loss is a difference between the TX power of abase station and the RX power of a terminal, and the TX power of thebase station may vary according to a TX antenna gain. When a beamwidthvaries, a maximum antenna gain of a main lobe varies. From the viewpointof a terminal, the variation of a beamwidth according to a beam patternused by a base station means the variation of a maximum TX antenna gain,and also means the variation of Effective Isotropic Radiated Power(EIRP). Thus, the terminal should be provided with a TX power value foreach beam pattern supported by the base station, and related informationfor calculation of the TX power value. Examples of the relatedinformation may include a maximum TX antenna gain for each beam pattern,an antenna gain, and base station TX power.

Yet another example of beam pattern information provided by a basestation is as follows. When resources for data transmission areallocated and different beam patterns are applied to the allocatedresources, a base station provides a terminal with resource allocationinformation in addition to beam pattern information. For example, when atime resource period is divided into a first period and a second periodand when a wide-beamwidth beam pattern is used in the first period and anarrow-beamwidth beam pattern is used in the second period, the basestation notifies terminals of the positions of the first period and thesecond period and the terminals detect the respective resource periodsand then perform smooth communication.

In summary, the beam pattern information provided by the base stationmay include at least one of information indicating the number of timesof transmitting a reference signal, related information for calculationof the number of times of transmitting the reference signal, a TX powervalue for each beam pattern, related information for calculation of theTX power value for each beam pattern, a maximum TX antenna gain for eachbeam pattern, and resource allocation information depending on anapplied beam pattern.

When the system operates a plurality of beam patterns in a unicastchannel, a base station should feed back related information from aterminal in order to determine an optimal beam pattern. Basically, inaddition to a Channel Quality Indicator (CQI) indicating the level of alink between the system and a terminal, the following items may befurther included.

When a path loss is very small because a terminal is located at asufficiently short distance from a base station, the improvement of linkRX power by a narrow beamwidth may not be necessary. When possible MIMOtransmission is suitable in a wide channel propagation environment, aunicast channel for the terminal may belong to a resource period using awide beamwidth. Thus, the terminal needs to notify the base station of apath loss value for each beam pattern of each beamwidth. Also, in orderfor the base station to determine an optimal beam pattern, the terminalmay feed back a preferred beam pattern among a plurality of beampatterns operated in the system, a beam direction, and the like. Also,when a channel interference is small, since the improvement of link RXpower by a narrow beamwidth is not necessarily required, the terminalneeds to notify an interference amount to the base station.

In summary, the feedback information of the terminal may include atleast one of a CQI, a path loss for each beam pattern, a preferred beampattern, a preferred beam direction, a CQI for each beam pattern ordirection, and an interference amount.

As described above, when a terminal feeds back information of aplurality of items, the feedback periods of the respective items may bedifferent from each other. For example, the feedback periods may be setdifferently according to the statistics of the value change frequenciesof the respective items. For example, the item with afrequently-changing value may be fed back at relatively short periods,and the item with a rarely-changing value may be fed back at relativelylong periods. As a specific example, the interference amount may be fedback at longer periods than the CQI. As another example, the preferredbeam direction may be fed back at longer periods than the CQI.

As described above, a terminal may feed back a CQI. The CQI may be atleast one of a Carrier-to-Interference and Noise Ratio (CINR), aSignal-to-Interference and Noise Ratio (SINR), a Signal-to-Noise Ratio(SNR), or the like, and may be related to a received signal strength.Also, the CQI may be related to an interference strength. Thus, sincethe CQI varies as a beam pattern changes, a base station should obtainCQI information for each beam pattern.

According to an exemplary embodiment of the present invention, aterminal may measure CQIs for all beam patterns and feed back all theCQIs for the respective beam patterns. In this case, a structure of areference signal for measurement of a CQI may be the same as thatdescribed below with reference to FIG. 5.

FIG. 5 illustrates examples of reference signal and channel informationfeedback in a wireless communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 5, a frame is divided into a downlink period 510 andan uplink period 520. In FIG. 5, the downlink period 510 and the uplinkperiod 520 are divided in a time axis. However, according to anotherexemplary embodiment of the present invention, the downlink period 510and the uplink period 520 may be divided in a frequency axis. FIG. 5assumes the case where three zones are defined for respective beampatterns. For example, a zone A 511 may be a period in which anisotropic beam pattern radiated uniformly in all directions is applied,a zone B 512 may be a period in which a wide-beamwidth beam pattern isapplied, and a zone C 513 may be a period in which a narrow-beamwidthbeam pattern is applied.

As illustrated in FIG. 5, the zone A 511, the zone B 512, and the zone C513 all include a reference signal period 517. A base station transmitsone or more reference signals beamformed by a beam pattern of therelevant zone through the reference signal period 517. In this case, thenumber of reference signals transmitted may be determined according to abeamwidth. For example, as a beamwidth decreases, a larger number ofreference signals may be transmitted. Accordingly, a terminal measures aCQI for each beam pattern by using a reference signal received throughthe reference signal period 517 of each of the zones 511, 512 and 513.In this case, through information received from the base station, theterminal detects the position of each of the zones 511, 512 and 513 andthe number of times of transmitting a reference signal in each zone.Then, in the uplink period 520, the terminal feeds back CQI informationfor each zone through a feedback channel 525.

In the exemplary embodiment described with reference to FIG. 5, thereference signals using the respective beam patterns are transmitted formeasurement of the CQIs for all the beam patterns. Thus, overhead due toa reference signal and overhead of CQI information may be large. Inorder to reduce the above-identified overhead, only reference signalsfor some beam patterns may be transmitted. In another exemplaryembodiment, reference signals for some beam patterns may be transmittedat predetermined periods, and reference signals for the other beampatterns may be transmitted at relatively long periods. For example,from the viewpoint of a specific time point, it is observed that onlyreference signals for some beam patterns are transmitted. An exemplaryembodiment in which only reference signals for some beam patterns aretransmitted is described below with reference to FIG. 6.

FIG. 6 illustrates examples of reference signal and channel informationfeedback in a wireless communication system according to anotherexemplary embodiment of the present invention.

Referring to FIG. 6, a frame is divided into a downlink period 610 andan uplink period 620. In FIG. 6, the downlink period 610 and the uplinkperiod 620 are divided in a time axis. However, according to anotherexemplary embodiment of the present invention, the downlink period 610and the uplink period 620 may be divided in a frequency axis. FIG. 6assumes the case where three zones are defined for respective beampatterns. For example, a zone A 611 may be a period in which anisotropic beam pattern radiated uniformly in all directions is applied,a zone B 612 may be a period in which a wide-beamwidth beam pattern isapplied, and a zone C 613 may be a period in which a narrow-beamwidthbeam pattern is applied.

As illustrated in FIG. 6, among the zone A 611, the zone B 612 and thezone C 613, only the zone A 611 includes a reference signal period 617.A base station transmits one or more reference signals beamformed by abeam pattern of the relevant zone through the reference signal period617. Accordingly, a terminal measures a CQI for a beam pattern appliedto the zone A 611 by using a reference signal received through thereference signal period 617 of the zone A 611. In this case, throughinformation received from the base station, the terminal detects theposition of each of the zones 611, 612 and 613 and the number of timesof transmitting a reference signal. Then, in the uplink period 620, theterminal feeds back CQI information for the zone A 611 through afeedback channel 625.

Since only CQI information for the zone A 611 is fed back, the basestation cannot know beam patterns applied to the zone B 612 and the zoneC 613. Thus, the terminal measures a downlink interference in each ofthe zones 611, 612 and 613 and provides information related to aninterference amount for each zone through the feedback channel 625, sothat the base station can calculate CQIs for beam patterns applied tothe zone B 612 and the zone C 613. For example, the terminal may measurethe interference by using pilot symbols transmitted in the zone B 612and the zone C 613 for equalization of data symbols. Herein, theinterference may be referred to as a Noise and Interference (NI), anInterference over Thermal (IoT), or the like. Accordingly, the basestation calculates a CQI of each zone by using a CQI for the zone A 611and an interference amount for each zone.

For example, a process of calculating the CQI of each zone is asfollows. Since the CQI is a signal-to-noise and interference ratio, whenan interference amount is known, the strength of a desired signal can becalculated. For example, the strength of a desired signal for a beampattern applied to the zone A 611 can be calculated by using a CQI forthe zone A 611 and an interference amount for the zone A 611. Then,since the base station knows a gain difference between beam patterns,the base station can calculate the strengths of desired signals for thebeam patterns applied to the zone B 612 and the zone C 613 from thestrength of a desired signal for the beam pattern applied to the zone A611, by considering the gain difference. Accordingly, the base stationknows both the interference amount and the strengths of desired signalsfor the beam patterns applied to the zone B 612 and the zone C 613, andthus can calculate CQIs for the zone B 612 and the zone C 613.

Referring to FIG. 6, CQI information for the zone A 611 and aninterference amount for each zone are transmitted through the feedbackchannel 625. Although not illustrated in FIG. 6, the CQI information andthe interference amount for each zone may be fed back at different timeintervals. For example, the interference amount for each zone may be fedback at longer periods than the CQI information. The reason for this isthat the interference does not greatly change for a long time ascompared to the CQI. Accordingly, as compared to the case of feedingback the CQI for each zone at short periods, the case of feeding backonly the CQI for one zone at short periods and feeding back informationrelated to an interference for each zone at long periods can reduce anoverall feedback overhead.

Also, in FIG. 6, since only the zone A 611 includes the reference signalperiod 617, an overhead due to a reference signal is reduced. As thebeamwidth decreases, the number of reference signals required increases.Therefore, in order to maximize the effect of overhead reduction, thereference signal period 617 may be included in the zone to which thewidest-beamwidth beam pattern is applied.

Also, in FIG. 6, only the zone A 611 includes the reference signalperiod 617. However, according to another exemplary embodiment of thepresent invention, the zone B 612 and the zone C 613 may also include areference signal period, and information fed back from the terminal maybe a CQI for the zone A 611 and an interference amount for each zone. Inthis case, as compared to the exemplary embodiment of FIG. 5, anoverhead due to a reference signal is the same but an amount of feedbackinformation is reduced.

Hereinafter, operations and configurations of a terminal and a basestation supporting a plurality of propagation characteristics accordingto an exemplary embodiment of the present invention will be described indetail with reference to the drawings.

FIG. 7 illustrates a process of operating a base station in a wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 7, in step 701, the base station selects one or morepropagation characteristics to be operated. The propagationcharacteristics may include at least one of characteristics of signalstransmitted/received through antennas, polarization characteristics, awave strength, and a beamwidth. For example, the base station selectspropagation characteristics to be supported for communication withterminals, in other words, candidates for propagation characteristicsused for communication. In this case, the base may consider acommunication environment of the base station. For example, if the basestation is a femto base station, the base station may determine tosupport only a wide-beamwidth beam pattern. According to anotherexemplary embodiment of the present invention, the base station mayselect one or more propagation characteristics to be operated, based onsetting information predefined by a designer or an operator.

In step 703, the base station determines a propagation characteristic tobe applied to each channel. Herein, the channel is divided according tothe purpose of a signal and data transmitted. For example, the channelmay be a broadcast channel for transmission of system data, asynchronization channel for transmission of a synchronization signal, adata channel for traffic transmission, or the like. In this case, thebase station may determine propagation characteristics based on therange of receivers of a signal or data transmitted through a relevantchannel, that is, for example, the number of receivers. For example,since the broadcast channel should be received by a plurality ofterminals, the base station may determine to apply a wide-beamwidth beampattern to the broadcast channel. As another example, since the datachannel should be received by one terminal, the base station maydetermine to apply a narrow-beamwidth beam pattern to the data channel.However, in order for the data channel to be adapted according to achannel environment of a terminal, the base station may determine toapply both a narrow-beamwidth beam pattern and a wide-beamwidth beampattern to the data channel.

In step 705, the base station allocates a resource period for eachpropagation characteristic. The resource period for each propagationcharacteristic is allocated in the data channel. For example, in orderto support various propagation characteristics in the data channel, thebase station allocates a resource period to which each propagationcharacteristic is applied. For example, as illustrated in FIG. 5 or 6,the base station may allocate a zone A, a zone B, and a zone C to whichbeam patterns with different beamwidths are applied. If supportingdifferent polarization characteristics, the base station may allocateresource periods for the different polarization characteristics suchthat they overlap each other in a frequency axis and a time axis.

In step 707, the base station generates system information onpropagation characteristics operated and transmits the systeminformation. In other words, the base station generates and transmitssystem information indicating the facts determined through steps 701 and703. Although not illustrated in FIG. 7, the system information may betransmitted periodically. Also, the system information may betransmitted through the broadcast channel. For example, the systeminformation may include at least one of information indicating anoperated propagation characteristic, information indicating the numberof times of transmitting a reference signal, a TX power value for eachpropagation characteristic, a maximum TX antenna gain for eachpropagation characteristic, resource allocation information for eachpropagation characteristic, information indicating a beam direction, andrelated information for determination of at least one of the listeditems.

In step 709, the base station transmits reference signals for channelquality measurement. The reference signals are transmitted through atleast one of the resource periods for respective propagationcharacteristics. According to an exemplary embodiment of the presentinvention, the base station may transmit reference signals withrespective propagation characteristics through respective resourceperiods for respective propagation characteristics with respect to allpropagation characteristics. According to another exemplary embodimentof the present invention, the base station may transmit referencesignals with relevant propagation characteristics through resourceperiods for relevant propagation characteristics with respect to somepropagation characteristics. In this case, the base station mayrepeatedly transmit the reference signal with the some propagationcharacteristic in different beam directions. Thus, in order to reduce anoverhead due to a reference signal, the some propagation characteristicsmay be transmitted in a wide beamwidth. Although not illustrated in FIG.7, the reference signals may be transmitted periodically.

In step 711, the base station receives feedback information related topropagation characteristics from one or more terminals. For example, thefeedback information may include at least one of a CQI, an interferenceamount, a path loss for each beam pattern, a preferred beam pattern, anda preferred beam direction. Herein, the CQI may be CQIs for therespective resource periods for respective propagation characteristics,or CQIs for some of the resource periods for respective propagationcharacteristics. When the feedback information includes only the CQIsfor some of the resource periods for respective propagationcharacteristics, the feedback information may include interferenceamount information on the other resource periods.

In step 713, the base station determines propagation characteristics tobe applied to the one or more terminals, with reference to the feedbackinformation. In this case, the base station considers channelenvironments of the one or more terminals determined through thefeedback information, a link quality, a preferred beam direction, a CQI,an LoS indication, polarization characteristics, and a path loss. Forexample, the base station may estimate a distance from a terminal and achannel environment (e.g., an LoS indication) based on the path loss.Also, the base station may determine an optimal beam pattern based onthe CQI. If the system information includes an interference and a CQIfor one or more beam patterns and only an interference for the otherbeam patterns, the base station may calculate CQIs for all the beampatterns by using the CQI and the interference. Specifically, when alink quality is higher than a threshold value, the base station maydetermine to apply a wide-beamwidth beam pattern to the relevantterminal. Also, in an LoS environment, the base station may determine toapply a specific polarization characteristic to the relevant terminal.

Although not illustrated in FIG. 7, the base station allocates resourcesto the one or more terminals according to the determination in step 713,and performs communication. Herein, the propagation characteristicsdetermined in step 713 may be changed according to the state of eachterminal. For example, when the path loss of a terminal is lower than athreshold value, the base station may change a beam pattern applied tothe terminal into a beam pattern with a wider beamwidth. For example,when the path loss of a terminal increases due to an obstacle, the basestation may change a beam direction of a beam pattern applied to theterminal or change the applied beam pattern into a beam pattern with awider beamwidth. For example, when the path loss of a terminal increasesdue to an increased distance from a base station, the base station maychange a beam pattern applied to the terminal into a beam pattern with anarrower beamwidth.

In the exemplary embodiment described with reference to FIG. 7, the basestation determines propagation characteristics for respective channelsand determines a resource period for each propagation characteristic.However, according to another exemplary embodiment of the presentinvention, at least one of step 703 for determining the propagationcharacteristics for respective channels and step 705 for determiningeach propagation characteristic may be omitted. For example, when thebase station does not apply propagation characteristics differentlyaccording to channels, step 703 may be omitted. Also, for example, whenthe base station determines to operate only one propagationcharacteristic in step 701, step 703 and step 705 may be omitted.

FIG. 8 illustrates a process of operating a terminal in a wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 8, in step 801, the terminal acquires synchronizationand receives system information. Specifically, the terminal acquiressynchronization with a base station by detecting a synchronizationchannel, and receives the system information through a broadcastchannel. The system information includes information on propagationcharacteristics operated in the base station. For example, the systeminformation may include at least one of information indicating apropagation characteristic operated in the base station, informationindicating the number of times of transmitting a reference signal, a TXpower value for each beam pattern or propagation characteristic, amaximum TX antenna gain for each beam pattern or propagationcharacteristic, resource allocation information for each propagationcharacteristic, and related information for determination of at leastone of the listed items.

In step 803, the terminal estimates a channel quality for each beampattern or propagation characteristic. The terminal estimates thechannel quality by using reference signals received from the basestation. In this case, the reference signals are applied with all orsome of the beam patterns or propagation characteristics operated in thebase station, and the reference signal applied with the beam pattern orpropagation characteristic is transmitted through a resource periodallocated for the relevant beam pattern or propagation characteristic.Thus, through the system information, the terminal determines a resourceperiod allocated for each beam pattern or propagation characteristic,whether a reference signal is transmitted in each resource period, andthe number of times of transmitting a reference signal, and then detectsa reference signal. According to an exemplary embodiment of the presentinvention, the reference signals may be transmitted in all of theresource periods. In this case, the terminal may measure CQIs for allthe beam patterns or the respective propagation characteristics. On theother hand, according to another exemplary embodiment of the presentinvention, the reference signals may be transmitted only in one or moreresource periods. In this case, the terminal may measure a CQI andinterference for one or more beam patterns or propagationcharacteristics and measure only an interference for the other beampatterns or propagation characteristics. According to yet anotherexemplary embodiment of the present invention, even when the referencesignals are transmitted in all the resource periods, the terminal maymeasure a CQI and interference for one or more beam patterns orpropagation characteristics and measure only an interference for theother beam patterns or propagation characteristics.

In step 805, the terminal estimates a path loss for each beam pattern orpropagation characteristic. The path loss may be estimated by using a TXpower value for each beam pattern or propagation characteristic includedin the system information received in step 801, or by using relatedinformation for calculation of the TX power value. For example, theterminal may detect a TX power value for each beam pattern orpropagation characteristic or calculate a TX power value for each beampattern or propagation characteristic by using the related information,and then may estimate the path loss by subtracting RX power from the TXpower.

In step 807, the terminal determines a preferred beam direction. Thereference signal transmitted by the base station may be repeatedlytransmitted with the same propagation characteristic in different beamdirections. Thus, the terminal attempts to detect a plurality ofreference signals of different beam directions while applying the samebeam pattern or propagation characteristic, and detects a plurality ofreference signals accordingly. In this case, the terminal may determinea TX beam direction applied to the reference signal with the strong RXsignal strength as a preferred TX beam direction. Also, the terminal maychange an RX beam and detect a signal of the same TX beam directionrepeatedly. In this case, the terminal may determine an RX beamdirection applied to the reference signal with the strong RX signalstrength as a preferred RX beam direction.

In step 809, the terminal generates feedback information and transmitsthe feedback information to the base station. The feedback informationincludes information used to determine a propagation characteristic tobe applied to the terminal by the base station. For example, thefeedback information is used to notify the facts determined throughsteps 803 to 807. For example, the feedback information may include atleast one of a CQI for one or more beam patterns or propagationcharacteristics, an interference amount for each beam pattern orpropagation characteristic, a path loss for each beam pattern orpropagation characteristic, a preferred beam pattern or propagationcharacteristic, a preferred beam direction, and a CQI for each preferredbeam pattern or beam direction. The feedback information may beperiodically transmitted at predetermined time intervals. In this case,information items included in the feedback information may vary. Forexample, the CQI and the interference amount are included, theinterference amount may be fed back at longer periods than the CQI.

In the exemplary embodiment described with reference to FIG. 8, theterminal estimates a channel quality for each beam pattern orpropagation characteristic, estimates a path loss for each beam patternor propagation characteristic, and determines a preferred beamdirection. However, according to another exemplary embodiment of thepresent invention, at least one of step 803 for estimating a channelquality for each beam pattern or propagation characteristic, step 805for estimating a path loss for each beam pattern or propagationcharacteristic, and step 807 for determining a preferred beam directionmay be omitted.

FIG. 9 illustrates a block configuration of a base station in a wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 9, the base station may include a modem 910, areceiving unit 920, a TX RF chain 930, beamforming units 940-1 and940-2, antenna arrays 950-1 and 950-2, and a control unit 960.

The modem 910 performs conversion between a baseband signal and abitstream according to a physical layer standard of the system. Forexample, according to an Orthogonal Frequency-Division Multiplexing(OFDM) scheme, in a data transmission mode, the modem 910 generatescomplex symbols by encoding/modulating a TX bitstream, maps the complexsymbols to subcarriers, and generates OFDM symbols by Inverse FastFourier Transform (IFFT) operation and Cyclic Prefix (CP) insertion.Also, in a data reception mode, the modem 910 divides a baseband signalinto OFDM symbols, restores signals mapped to subcarriers by FastFourier Transform (FFT) operation, and restores a received bitstream bydemodulation and decoding. The receiving unit 910 converts an RF signalreceived from a terminal into a baseband digital signal. Although notillustrated in the drawings, the receiving unit 920 may include anantenna and an RX RF chain.

The TX RF chain 930 converts a baseband digital signal stream receivedfrom the modem 910 into an RF analog signal. For example, the TX RFchain 930 may include an amplifier, a mixer, an oscillator, aDigital-to-Analog Converter (DAC), and a filter. FIG. 9 illustrates onlyone TX RF chain 930. However, according to another exemplary embodimentof the present invention, the base station includes a plurality of TX RFchains. In this case, the base station may simultaneously form aplurality of TX beams as many as the number of TX RF chains.

The beamforming units 940-1 and 940-2 perform TX beamforming on a TXsignal received from the TX RF chain 930. For example, each of thebeamforming units 940-1 and 940-2 includes a plurality of phaseshifters, a plurality of amplifiers, and a signal adder. For example,the beamforming units 940-1 and 940-2 divide a TX signal received fromthe TX RF chain 930 into signals as many as the number of antennasincluded in the antenna arrays 950-1 and 950-2, and adjust the phasesand amplitudes of the signals divided. The beamforming units 940-1 and940-2 correspond respectively to the antenna arrays 950-1 and 950-2.

Each of the antenna arrays 950-1 and 950-2 is a group of antennas, andincludes a plurality of array elements. The antenna arrays 950-1 and950-2 radiate signals received from the beamforming units 940-1 and940-2 to wireless channels. Herein, the first antenna array 950-1 andthe second antenna array 950-2 have different polarizationcharacteristics. For example, the first antenna array 950-1 generates acircular polarization and the second antenna array 950-2 generates alinear polarization. According to another exemplary embodiment of thepresent invention, an antenna array with a different polarizationcharacteristic may be added, or only one antenna array may be provided.

The control unit 960 controls an overall operation of the base station.For example, the control unit 960 generates a TX traffic packet andmessage and provides the same to the modem 910, and interprets an RXtraffic packet and message received from the modem 910. In particular,according to an exemplary embodiment of the present invention, thecontrol unit 960 controls to support a plurality of propagationcharacteristics. An operation of the control unit 960 for supporting theplurality of propagation characteristics will be described below.

The control unit 960 selects one or more propagation characteristics tobe operated, determines a propagation characteristic to be applied toeach channel, allocates a resource period for each propagationcharacteristic, and system information on a propagation characteristicoperated. For example, the system information may include at least oneof information indicating a propagation characteristic operated,information indicating the number of times of transmitting a referencesignal, a TX power value for each beam pattern, a maximum TX antennagain for each beam pattern, resource allocation information for eachpropagation characteristic, and related information for determination ofat least one of the listed items.

Then, the control unit 960 controls to transmit reference signals forchannel quality measurement. The reference signals are transmittedthrough at least one of the resource periods for respective propagationcharacteristics. According to an exemplary embodiment of the presentinvention, the control unit 960 may control to transmit referencesignals with respective propagation characteristics through respectiveresource periods for respective propagation characteristics with respectto all propagation characteristics. According to another exemplaryembodiment of the present invention, the control unit 960 may control totransmit reference signals with relevant propagation characteristicsthrough resource periods for relevant propagation characteristics withrespect to some propagation characteristics. In this case, the controlunit 960 may repeatedly transmit the reference signal with the samepropagation characteristic in different beam directions.

Also, the control unit 960 receives feedback information related topropagation characteristics from one or more terminals, and determinespropagation characteristics to be applied to the one or more terminalswith reference to the feedback information. In summary, the feedbackinformation may include at least one of a CQI, an interference amount, apath loss for each beam pattern, a preferred beam pattern, a preferredbeam direction, and a CQI for each preferred beam pattern or direction.If the system information includes an interference and a CQI for one ormore beam patterns and only an interference for the other beam patterns,the control unit 960 may calculate CQIs for all the beam patterns byusing the CQI and the interference. Also, the control unit 960 maychange a propagation characteristic applied according to the state ofeach terminal.

In the exemplary embodiment illustrated in FIG. 9, the base stationincludes only one TX RF chain 930. However, according to anotherexemplary embodiment of the present invention, the base station mayinclude a plurality of TX RF chains and include a digital precoder at afront end of the TX RF chains, instead of the beamforming units 940-1and 940-2, to perform digital beamforming. In addition, according to yetanother exemplary embodiment of the present invention, the base stationmay include both the beamforming units 940-1 and 940-2 and the digitalprecoder to perform hybrid beamforming. In this case, the beamformingunits 940-1 and 940-2 may further perform an operation of adding signalsto be transmitted through the same antennas, among thedigital-beamformed signals.

FIG. 10 illustrates a block configuration of a terminal in a wirelesscommunication system according to an exemplary embodiment of the presentinvention.

Referring to FIG. 10, the terminal may include an antenna array 1010, abeamforming unit 1020, an RX RF chain 1030, a modem 1040, a transmittingunit 1050, and a control unit 1060.

The antenna array 1010 is a group of a plurality of antennas, andincludes a plurality of array elements. The beamforming unit 1020performs RX beamforming on a signal received through a plurality ofantennas included in the antenna array 1010. For example, thebeamforming unit 1020 includes a plurality of amplifiers, a plurality ofphase shifters, and a signal adder. For example, the beamforming unit1020 performs RX beamforming by adjusting the phases of signals receivedthrough the respective antennas and adding the same. The RX RF chain1030 converts an RF analog RX signal into a baseband digital signal. Forexample, the RX RF chain 1030 may include an amplifier, a mixer, anoscillator, an Analog-to-Digital Converter (ADC), and a filter. FIG. 10illustrates only one RX RF chain 1030. However, according to anotherexemplary embodiment of the present invention, the terminal may includea plurality of RX RF chains. In this case, the terminal maysimultaneously form a plurality of RX beams as many as the number of RXRF chains.

The modem 1040 performs conversion between a baseband signal and abitstream according to a physical layer standard of the system. Forexample, according to an OFDM scheme, in a data transmission mode, themodem 1040 generates complex symbols by encoding/modulating a TXbitstream, maps the complex symbols to subcarriers, and generates OFDMsymbols by IFFT operation and CP insertion. Also, in a data receptionmode, the modem 1040 divides a baseband signal received from the RX RFchain 1030 into OFDM symbols, restores signals mapped to subcarriers byFFT operation, and restores a received bitstream by demodulation anddecoding.

In particular, the modem 1040 measures received signal strengths ofsynchronization signals transmitted from a base station. Specifically,the modem 1040 detects reference signals transmitted from the basestation. Also, the modem 1040 measures a received signal strength of thedetected reference signal and provides the received signal strength tothe control unit 1060. Also, the modem 1040 estimates a channel qualityfor each beam pattern by using the reference signals. According to anexemplary embodiment of the present invention, when the referencesignals are transmitted in all of the resource periods allocated for therespective propagation characteristics, the modem 1040 may measure CQIsfor the respective beam patterns. On the other hand, according toanother exemplary embodiment of the present invention, when thereference signals are transmitted only in one or more resource periods,the modem 1040 may measure a CQI and interference for one or more beampatterns and measure only an interference for the other beam patterns.According to yet another exemplary embodiment of the present invention,even when the reference signals are transmitted in all the resourceperiods, the modem 1040 may measure a CQI and interference for one ormore beam patterns and measure only an interference for the other beampatterns.

The transmitting unit 1050 converts a TX signal received from the modem1040 into an RX signal and transmits the same to the base station.Although not illustrated in the drawings, the transmitting unit 1050 mayinclude a TX RF chain and an antenna.

The control unit 1060 controls an overall operation of the terminal. Forexample, the control unit 1060 generates a TX traffic packet and messageand provides the same to the modem 1040, and interprets an RX trafficpacket and message received from the modem 1040. In particular, thecontrol unit 1060 controls to generate feedback information onpropagation characteristics for communication with a base stationsupporting a plurality of propagation characteristics, and transmit thefeedback information. An operation of the control unit 1060 forgenerating/transmitting the feedback information will be describedbelow.

The control unit 1060 obtains information on propagation characteristicsoperated by a base station through system information received from thebase station. For example, the system information may include at leastone of information indicating a propagation characteristic operated inthe base station, information indicating the number of times oftransmitting a reference signal, a TX power value for each beam pattern,a maximum TX antenna gain for each beam pattern, resource allocationinformation for each propagation characteristic, and related informationfor determination of at least one of the listed items. Then, the controlunit 1060 controls the modem 1040 to determine, through the systeminformation, a resource period allocated for each beam pattern, whethera reference signal is transmitted in each resource period, and thenumber of times of transmitting a reference signal, and then detect areference signal.

The control unit 1060 estimates a path loss for each beam pattern. Thepath loss may be estimated by using a TX power value for each beampattern included in the system information, or by using relatedinformation for calculation of the TX power value. Also, the controlunit 1060 determines a preferred beam direction. Specifically, thecontrol unit 1060 may determine a TX beam direction applied to thereference signal with the strong RX signal strength as a preferred TXbeam direction, and may determine an RX beam direction applied to thereference signal with the strong RX signal strength as a preferred RXbeam direction.

The control unit 1060 generates feedback information, and transmits thefeedback information to the base station through the transmitting unit1050. For example, the feedback information may include at least one ofa CQI for one or more beam patterns, an interference amount for eachbeam pattern, a path loss for each beam pattern, a preferred beampattern, a preferred beam direction, and a CQI for each preferred beampattern or direction. The feedback information may be periodicallytransmitted at predetermined time intervals, and information itemsincluded in the feedback information may vary. For example, the CQI andthe interference amount are included, the interference amount may be fedback at longer periods than the CQI.

In the exemplary embodiment illustrated in FIG. 10, the terminalincludes only one RX RF chain 1030. However, according to anotherexemplary embodiment of the present invention, the terminal may includea plurality of RX RF chains and include a digital postcoder at a rearend of the RX RF chains, instead of the beamforming unit 1020, toperform digital beamforming. In addition, according to yet anotherexemplary embodiment of the present invention, the terminal may includeboth the beamforming unit 1020 and the digital postcoder to performhybrid beamforming.

Signals with various propagation characteristics are used in a wirelesscommunication system operating based on beamforming. Thus, it ispossible to transmit a signal with a propagation characteristic suitablefor the characteristic of each channel operated in the system and asignal with a propagation characteristic suitable for the link/channelcharacteristics of a base station and a terminal. Accordingly, overheadcan be reduced through transmission of a signal optimized for eachchannel, and the transmission efficiency of a data channel can bemaximized. Consequently, overall system performance can be improved.

It will be appreciated that embodiments of the present inventionaccording to the claims and description in the specification can berealized in the form of hardware, software or a combination of hardwareand software.

Any such software may be stored in a computer readable storage medium.The computer readable storage medium stores one or more programs(software modules), the one or more programs comprising instructions,which when executed by one or more processors in an electronic device,cause the electronic device to perform a method of the presentinvention.

Any such software may be stored in the form of volatile or non-volatilestorage such as, for example, a storage device like a ROM, whethererasable or rewritable or not, or in the form of memory such as, forexample, RAM, memory chips, device or integrated circuits or on anoptically or magnetically readable medium such as, for example, a CD,DVD, magnetic disk or magnetic tape or the like. It will be appreciatedthat the storage devices and storage media are embodiments ofmachine-readable storage that are suitable for storing a program orprograms comprising instructions that, when executed, implementembodiments of the present invention.

Accordingly, embodiments provide a program comprising code forimplementing apparatus or a method as claimed in any one of the claimsof this specification and a machine-readable storage storing such aprogram. Still further, such programs may be conveyed electronically viaany medium such as a communication signal carried over a wired orwireless connection and embodiments suitably encompass the same.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for operating a base station in awireless communication system, the method comprising: allocatingresource periods for respective propagation characteristics;transmitting system information including information on the propagationcharacteristics; transmitting a reference signal with the propagationcharacteristic corresponding to the relevant resource period through atleast one of the resource periods; and receiving feedback informationdetermining channel qualities for at least one of the propagationcharacteristics.
 2. The method of claim 1, wherein the systeminformation includes at least one of information indicating thepropagation characteristics to be operated, allocation information ofthe resource periods, information indicating a number of times oftransmitting the reference signal, a transmission (TX) power value foreach propagation characteristic, a maximum TX antenna gain for eachpropagation characteristic, information indicating a beam direction, andrelated information for determination of at least one of the listeditems.
 3. The method of claim 1, wherein the feedback informationincludes at least one of a Channel Quality Indicator (CQI) for each ofthe propagation characteristics, a path loss for each propagationcharacteristic, a preferred propagation characteristic, a preferred beamdirection, a CQI for each beam direction, and an interference amount. 4.The method of claim 3, wherein the feedback information is transmittedperiodically, and feedback periods for respective items included in thefeedback information are different from each other.
 5. The method ofclaim 1, wherein the feedback information includes at least one of aChannel Quality Indicator (CQI) and an interference amount for one ormore propagation characteristics among the propagation characteristics,an interference amount for the other propagation characteristics, apreferred propagation characteristic, and a preferred beam direction. 6.The method of claim 5, further comprising determining the CQI for eachof the propagation characteristics by using the CQI and the interferenceamount for the one or more propagation characteristics and theinterference amount for the other propagation characteristics.
 7. Themethod of claim 1, wherein the reference signal is transmitted througheach of the resource periods.
 8. The method of claim 1, wherein thereference signal is transmitted through at least one of the resourceperiods.
 9. The method of claim 1, further comprising determiningpropagation characteristics to be applied to different types ofchannels.
 10. The method of claim 9, wherein the determining of thepropagation characteristics to be applied to different types of channelscomprises determining to apply a wide-beamwidth beam pattern to achannel for transmission of a signal that is to be received by aplurality of terminals.
 11. The method of claim 1, further comprisingdetermining a propagation characteristic to be applied to at least oneterminal by using the feedback information.
 12. The method of claim 11,wherein the determining of the propagation characteristic to be appliedto at least one terminal comprises determining, if a link quality of aterminal is equal to or higher than a threshold value, to apply awide-beamwidth beam pattern to the terminal.
 13. The method of claim 11,wherein the determining of the propagation characteristic to be appliedto the at least one terminal comprises determining, if a terminal is ina Line-of-Sight (LoS) environment, to apply a propagation characteristicdifferent from a propagation characteristic of at least one differentterminal to the terminal.
 14. The method of claim 11, further comprisingchanging the propagation characteristic applied to the at least oneterminal.
 15. The method of claim 14, wherein the changing of thepropagation characteristic applied to the at least one terminalcomprises changing, if a path loss of a terminal is lower than athreshold value, a beam pattern applied to the terminal into a beampattern with a narrower beamwidth.
 16. The method of claim 14, whereinthe changing of the propagation characteristic applied to the at leastone terminal comprises changing, if a path loss of a terminal increasesdue to an obstacle, changing a beam direction of a beam pattern appliedto the terminal.
 17. The method of claim 14, wherein the changing of thepropagation characteristic applied to the at least one terminalcomprises changing, if a path loss of a terminal increases due to anobstacle, changing a beam pattern applied to the terminal into a beampattern with a wider beamwidth.
 18. The method of claim 14, wherein thechanging of the propagation characteristic applied to the at least oneterminal comprises changing, if a path loss of a terminal increases dueto an increased distance from the base station, changing a beam patternapplied to the terminal into a beam pattern with a narrower beamwidth.19. A method for operating a terminal in a wireless communicationsystem, the method comprising: receiving system information includinginformation on propagation characteristics operated in a base station;detecting an allocation of resource periods for the propagationcharacteristics through the system information; detecting a referencesignal with a propagation characteristic corresponding to a relevantresource period through at least one of the resource periods; andtransmitting feedback information determining channel qualities for atleast one of the propagation characteristics.
 20. The method of claim19, wherein the system information includes at least one of informationindicating the propagation characteristics to be operated, allocationinformation of the resource periods, information indicating a number oftimes of transmitting the reference signal, a transmission (TX) powervalue for each propagation characteristic, a maximum TX antenna gain foreach propagation characteristic, information indicating a beamdirection, and related information for determination of at least one ofthe listed items.
 21. The method of claim 20, further comprising:determining a TX power value for each propagation characteristic throughthe system information; and estimating a path loss for each propagationcharacteristic by using the TX power value for each propagationcharacteristic, wherein the feedback information includes the path lossfor each propagation characteristic.
 22. The method of claim 19, whereinthe feedback information includes at least one of a Channel QualityIndicator (CQI) for each of the propagation characteristics, a path lossfor each propagation characteristic, a preferred propagationcharacteristic, a preferred beam direction, a CQI for each beamdirection, and an interference amount.
 23. The method of claim 22,wherein the feedback information is transmitted periodically, andfeedback periods for respective items included in the feedbackinformation are different from each other.
 24. The method of claim 19,wherein the feedback information includes at least one of a ChannelQuality Indicator (CQI) and an interference amount for one or morepropagation characteristics among the propagation characteristics, aninterference amount for the other propagation characteristics, apreferred propagation characteristic, and a preferred beam direction.25. The method of claim 19, wherein the reference signal is transmittedthrough each of the resource periods.
 26. The method of claim 19,wherein the reference signal is transmitted through at least one of theresource periods.
 27. The method of claim 19, further comprisingdetermining a preferred beam direction by using a received signalstrength of the reference signal, wherein the feedback informationincludes information indicating the preferred beam direction.
 28. Anapparatus of a base station in a wireless communication system, theapparatus comprising: a control unit configured to allocate resourceperiods for respective propagation characteristics; and a modemconfigured to transmit system information including information on thepropagation characteristics, transmitting a reference signal with thepropagation characteristic corresponding to the relevant resource periodthrough at least one of the resource periods, and configured to receivefeedback information determining channel qualities for at least one ofthe propagation characteristics.
 29. The apparatus of claim 28, whereinthe system information includes at least one of information indicatingthe propagation characteristics to be operated, allocation informationof the resource periods, information indicating a number of times oftransmitting the reference signal, a transmission (TX) power value foreach propagation characteristic, a maximum TX antenna gain for eachpropagation characteristic, information indicating a beam direction, andrelated information for determination of at least one of the listeditems.
 30. The apparatus of claim 28, wherein the feedback informationincludes at least one of a Channel Quality Indicator (CQI) for each ofthe propagation characteristics, a path loss for each propagationcharacteristic, a preferred propagation characteristic, a preferred beamdirection, a CQI for each beam direction, and an interference amount.31. The apparatus of claim 30, wherein the feedback information istransmitted periodically, and feedback periods for respective itemsincluded in the feedback information are different from each other. 32.The apparatus of claim 28, wherein the feedback information includes atleast one of a Channel Quality Indicator (CQI) and an interferenceamount for one or more propagation characteristics among the propagationcharacteristics, an interference amount for the other propagationcharacteristics, a preferred propagation characteristic, and a preferredbeam direction.
 33. The apparatus of claim 32, wherein the control unitdetermines the CQI for each of the propagation characteristics by usingthe CQI and the interference amount for the one or more propagationcharacteristics and the interference amount for the other propagationcharacteristics.
 34. The apparatus of claim 28, wherein the referencesignal is transmitted through each of the resource periods.
 35. Theapparatus of claim 28, wherein the reference signal is transmittedthrough at least one of the resource periods.
 36. The apparatus of claim28, wherein the control unit determines propagation characteristics tobe applied to different types of channels.
 37. The apparatus of claim36, wherein the control unit determines to apply a wide-beamwidth beampattern to a channel for transmission of a signal that is to be receivedby a plurality of terminals.
 38. The apparatus of claim 28, wherein thecontrol unit determines a propagation characteristic to be applied to atleast one terminal by using the feedback information.
 39. The apparatusof claim 38, wherein, if a link quality of a terminal is equal to orhigher than a threshold value, the control unit determines to apply awide-beamwidth beam pattern to the terminal.
 40. The apparatus of claim38, wherein, if a terminal is in a Line-of-Sight (LoS) environment, thecontrol unit determines to apply a propagation characteristic differentfrom a propagation characteristic of at least one different terminal tothe terminal.
 41. The apparatus of claim 38, wherein the control unitchanges the propagation characteristic applied to the at least oneterminal.
 42. The apparatus of claim 41, wherein, if a path loss of aterminal is lower than a threshold value, the control unit changes abeam pattern applied to the terminal into a beam pattern with a narrowerbeamwidth.
 43. The apparatus of claim 41, wherein, if a path loss of aterminal increases due to an obstacle, the control unit changes a beamdirection of a beam pattern applied to the terminal.
 44. The apparatusof claim 41, wherein, if a path loss of a terminal increases due to anobstacle, the control unit changes a beam pattern applied to theterminal into a beam pattern with a wider beamwidth.
 45. The apparatusof claim 41, wherein, if a path loss of a terminal increases due to anincreased distance from the base station, the control unit changes abeam pattern applied to the terminal into a beam pattern with a narrowerbeamwidth.
 46. A terminal in a wireless communication system, theterminal comprising: a modem configured to receive system informationincluding information on propagation characteristics operated in a basestation; and a control unit configured to detect an allocation ofresource periods for the propagation characteristics through the systeminformation, wherein the modem detects a reference signal with apropagation characteristic corresponding to a relevant resource periodthrough at least one of the resource periods, and transmits feedbackinformation determining channel qualities for at least one of thepropagation characteristics.
 47. The terminal of claim 46, wherein thesystem information includes at least one of information indicating thepropagation characteristics to be operated, allocation information ofthe resource periods, information indicating a number of times oftransmitting the reference signal, a transmission (TX) power value foreach propagation characteristic, a maximum TX antenna gain for eachpropagation characteristic, information indicating a beam direction, andrelated information for determination of at least one of the listeditems.
 48. The terminal of claim 47, wherein the control unit determinesa TX power value for each beam pattern through the system informationand estimates a path loss for each beam pattern by using the TX powervalue for each beam pattern, wherein the feedback information includesthe path loss for each beam pattern.
 49. The terminal of claim 46,wherein the feedback information includes at least one of a ChannelQuality Indicator (CQI) for each of the propagation characteristics, apath loss for each propagation characteristic, a preferred propagationcharacteristic, a preferred beam direction, a CQI for each beamdirection, and an interference amount.
 50. The terminal of claim 49,wherein the feedback information is transmitted periodically, andfeedback periods for respective items included in the feedbackinformation are different from each other.
 51. The terminal of claim 46,wherein the feedback information includes at least one of a ChannelQuality Indicator (CQI) and an interference amount for one or morepropagation characteristics among the propagation characteristics, aninterference amount for the other propagation characteristics, apreferred propagation characteristic, and a preferred beam direction.52. The terminal of claim 46, wherein the reference signal istransmitted through each of the resource periods.
 53. The terminal ofclaim 46, wherein the reference signal is transmitted through at leastone of the resource periods.
 54. The terminal of claim 46, wherein thecontrol unit determines a preferred beam direction by using a receivedsignal strength of the reference signal, wherein the feedbackinformation includes information indicating the preferred beamdirection.